1. Technical Field
The present invention relates to an electric circuit for rectifying an alternating current, more particularly to an electric circuit for rectifying an alternating current with a small loss.
2. Background Art
A rectification circuit has been used as a circuit for converting an alternating voltage to a direct voltage.
The conventional rectification circuit is comprised of a silicon diode, a schottky-barrier diode, or the like.
In the conventional circuit, however, a forward voltage Vf of a diode is approximately 0.4V to 1.0V, as shown in FIG. 3 showing a relationship between the voltage Vf and a current If. Therefore, the voltage drop, in other words, a loss in the diode of the rectification circuit, is large. As a result, inefficient rectification has been a problematical matter.
The present invention has been made in consideration of the above, and it is an object of the present invention to provide an electric circuit which can rectify an alternating current with a small loss.
To achieve the above described object, an electric circuit according to a first aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and is controlled by said control circuit to be activated or inactivated to output a rectified voltage at the other end of said current path; and
said control circuit is connected to at least one end of said current path of said transistor and said control terminal, activates said transistor when a reverse voltage is applied to said current path, inactivates said transistor when a forward voltage is applied to said current path, and controls a signal to be applied to said control terminal for activating or inactivating said transistor to make said transistor rectify said target voltage.
According to the electric circuit of the first aspect of the present invention, the transistor is activated when the voltage applied to the current path of the transistor is a reverse voltage, and is inactivated when it is a forward voltage. Therefore, only a voltage having one polarity is applied to a load which is connected to the transistor. And, a forward voltage is applied to the current path when the transistor is inactivated, therefore, a high withstanding voltage can be obtained.
The electric circuit according to a second aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and outputs a rectified voltage at the other end of said current path by being activated or inactivated in accordance with control of said control circuit; and
said control circuit is connected to both ends of said current path and said control terminal, detects the potential difference between the both ends of said current path, and controls a signal to be applied to said control terminal for activating or inactivating said transistor, so as to activate said transistor when a reverse voltage of said transistor is applied to said current path of said transistor and inactivate said transistor when a forward voltage of said transistor is applied to said current path, to make said transistor rectify said target voltage.
The electric circuit according to a third aspect comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and outputs a rectified voltage to the other end of said current path by being activated or inactivated in accordance with control of said control circuit; and
said control circuit is connected to both ends of said current path and said control terminal, detects the potential difference between the both ends of said current path, and controls a signal to be applied to said control terminal for activating or inactivating said transistor so as to activate said transistor when a reverse voltage is applied to said current path of said transistor and inactivate said transistor when a forward voltage is applied to said current path to make said transistor rectify said target voltage.
According to the electric circuit of the second and third aspects of the present invention, the voltage which is applied between the both ends of the current path of the transistor or the polarity of the voltage is detected, and the transistor is activated when the voltage is in the reverse direction and the transistor is inactivated when the voltage is in the forward direction. Therefore, only voltage in one polarity is applied to a load which is connected to the other end side of the current path of the transistor. And, the forward voltage is applied to the current path when the transistor is inactivated, therefore, a high withstanding voltage can be obtained.
In thus structured electric circuit, there is a way to activate/inactivate the transistor based on values for the supplied target voltage to be rectified or its polarity. However, a reverse current flow is caused by this method because the source voltage becomes lower than the voltage at the load while the transistor is being activated, when a capacitor or a battery is used as the load retaining the voltage. By the present invention, the target voltage to be rectified can be rectified without such a problem because the voltage to be applied to the current path of the transistor is detected.
Said transistor is, for example, a bipolar transistor. In this case, both ends of said current path are the emitter and collector of said bipolar transistor, said control terminal is the base of said bipolar transistor, and said control circuit comprises means for detecting voltage and/or its polarity between said emitter and said collector, and for supplying a voltage and a current to said base.
If said bipolar transistor is an NPN type bipolar transistor:
one end of said current path is emitter of said NPN bipolar transistor, the other end of said current path is collector of said NPN bipolar transistor, and said control terminal is base of said NPN bipolar transistor; and
said control circuit supplies a voltage and a current for activating said NPN transistor to said base when potential in positive polarity, which is higher than that applied to said collector, is applied to said emitter, and supplies a voltage and a current for inactivating said NPN transistor to said base when voltage in positive polarity, which is lower than that applied to said collector, is applied to said emitter.
If said bipolar transistor is a PNP type bipolar transistor:
one end of said current path is emitter of said PNP bipolar transistor, the other end of said current path is collector of said PNP bipolar transistor, and said control terminal is base of said PNP bipolar transistor; and
said control circuit supplies a voltage and a current for activating said PNP transistor to said base when potential in positive polarity, which is higher than that applied to said emitter, is applied to said collector, and supplies a voltage and a current for inactivating said PNP transistor to said base when voltage in positive polarity, which is lower than that applied to said emitter, is applied to said collector.
Said bipolar transistor comprises the emitter and the collector both having substantially the same thickness of semiconductor layers. According to such a structure, the emitter and the collector are not distinguished substantially, and it can save current amplification factor largely during activation. Moreover, high withstanding voltage can be obtained.
Said transistor may be replaced with a field effect transistor.
In this case, both ends of said current path are source and drain of said field effect transistor, said control terminal is gate of said field effect transistor, and said control circuit comprises means for detecting voltage and/or its polarity between said source and said drain, and for applying a control voltage to said gate in accordance with the detected voltage.
If said field effect transistor is an N-channel type field effect transistor:
one end of said current path is source of said N-channel field effect transistor, the other end of said current path is drain of said N-channel field effect transistor, and said control terminal is gate of said N-channel field effect transistor; and
said control circuit comprises means for applying an activation voltage to said gate when voltage in positive polarity, which is higher than that applied to said drain, is applied to said source, and for supplying an inactivation voltage to said gate when voltage in positive polarity, which is lower than that applied to said drain, is applied to said source.
If said field effect transistor is a P-channel type field effect transistor;
said control circuit comprises means for applying voltage for activating said P-channel field effect transistor to said gate when voltage in positive polarity, which is lower than that applied to said drain, is applied to said source, and applying voltage for inactivating said P-channel field effect transistor to said gate when voltage in positive polarity, which is higher than that applied to said drain, is applied to said source.
Said control circuit comprises, for example, an amplification circuit, such as an operational amplifier, whose one input terminal is connected to one end of said current path of said transistor, whose other input terminal is connected to the other end of the current path of said transistor, and whose output terminal is connected to said control terminal of said transistor. In this case, a diode, which is connected parallel in reverse between said one and the other input terminals of said amplification circuit, and a constant current source, which is inserted between said one input terminal and the one end of said current path or between said other input terminal and the other end of said current path, may be further disposed thereon.
The operational amplifier may be one which performs as not only an amplifier but also a comparator. In other words, it may be one whose output voltage is saturated in accordance with input voltage.
The electric circuit according to a fourth aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and is controlled by said control circuit to be activated and inactivated to output a rectified voltage to the other end of said current path; and
said control circuit is connected to said current path and said control terminal of said transistor, and controls a signal to be applied to said control terminal in accordance with the direction of the current flowing through a node between one end of said current path and an external circuit, for activating or inactivating said transistor to make said transistor rectify said target voltage.
In the electric circuit according to the fourth aspect of the present invention, the transistor is activated and inactivated in accordance with the direction of the current flowing at the connection node between the current path of the transistor and the external circuit. When the transistor is activated, said current flows via the current path of the transistor and is supplied to a load circuit. Therefore, the rectified current can be applied to the load. Moreover, because forward voltage is applied when the transistor is inactivated, high withstanding voltage can be obtained.
Said transistor is, for example, a bipolar transistor. In this case, both ends of said current path are emitter and collector of said bipolar transistor, and said control terminal is base of said bipolar transistor. Said control circuit supplies a voltage and a current to said base, and activates said bipolar transistor.
If said bipolar transistor is an NPN type bipolar transistor;
one end of said current path is emitter of said NPN bipolar transistor, the other end of said current path is collector of said NPN bipolar transistor, and said control terminal is base of said bipolar transistor. Said control circuit detects the direction of the current flowing at a node between said emitter and said external circuit, and supplies a voltage and a current for activating said NPN transistor when the current in the predetermined direction is detected.
In this case, a diode may be connected between said emitter and said collector or between said emitter and said base so that the current in the predetermined direction flow at said node even if said NPN bipolar transistor is not activated.
If said bipolar transistor is a PNP type bipolar transistor;
one end of said current path is emitter of said PNP bipolar transistor, the other end of said current path is collector of said PNP bipolar transistor, and said control terminal is base of said PNP bipolar transistor. Said control circuit detects the direction of the current flowing at the node between said emitter and said external circuit, and supplies a voltage and a current for activating said PNP transistor to said base when the current in the predetermined direction are detected.
In those cases, a diode may be connected between said emitter and said collector or between said emitter and said base so that the current in the predetermined direction flow at said node even if said NPN bipolar transistor is not activated.
Said transistor is, for example, a field effect transistor;
both ends of said current path are source and drain of said field effect transistor, and said control terminal is gate of said field effect transistor; and
said control circuit comprises means for applying the gate voltage, which activates said field effect transistor in an area, to said gate.
If said field effect transistor is an N-channel type field effect transistor, for example, one end of said current path is source of said N-channel field effect transistor, the other end is drain of said N-channel field effect transistor, and said control terminal is gate of said field effect transistor. Said control circuit comprises means for applying voltage, which activate said N-channel field effect transistor, to said gate when the current flowing at the node between said source and said external circuit are in the predetermined direction.
If said field effect transistor is the N-channel type field effect transistor, said control circuit comprises means for detecting, for example, the current flowing from said source to said drain via a parasitic diode to activate said N-channel field effect transistor.
A diode may be connected between said source and said drain, or a voltage regulation diode may be connected between said gate and said source.
If said field effect transistor is a P-channel type field effect transistor, for example, one end of said current path is source of said P-channel field effect transistor, the other end thereof is drain of said P-channel field effect transistor, and said control terminal is gate of said P-channel field effect transistor. Said control circuit comprises means for applying voltage, which activates said P-channel field effect transistor, to said gate when the current flowing at the node between said source and said external circuit are in the predetermined direction.
Said control circuit may comprise means for detecting a current flowing from said drain to said source via a parasitic diode of said P-channel field effect transistor to activate said P-channel field effect transistor.
In those cases, a diode may be connected between said source and said drain, or a voltage regulation diode may be connected between said gate and said source.
Said control circuit comprises, for example, a transformer having a primary winding which is connected to one end of said current path of said transistor and a secondary winding which is magnetically connected to said primary winding, and a bias circuit which is connected to said secondary winding of said transformer and controls a signal to be supplied to said control terminal of said transistor in accordance with current which is generated at said secondary winding.
Said control circuit may comprise, for example, means for converting the inductive current at said secondary winding into a voltage signal to apply it to said control terminal. In this case, said control circuit comprises, for example, a conversion circuit for converting said inductive current at the secondary winding into a voltage signal, and means for amplifying the voltage signal converted by said conversion circuit and applying the amplified signal to said control terminal of said transistor.
Said control circuit comprises, for example, an active element which requires electricity, and said rectified voltage is supplied to said active element as the electricity.
The electric circuit according to a fifth aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path from the power source, is connected to a resistance load via the other end of said current path, and is controlled by said control circuit to be activated and inactivated to output a rectified voltage to the other end of said current path; and
a predetermined reference potential is applied to said control terminal.
This is a very simple structure, however, the rectified voltage can be applied to the resistance road.
For example, said control terminal of said transistor, said power source, and said load are grounded at a substantially common point.
It is to be desired that said control circuit should activate said transistor under its saturation. Under the saturation, the emitter and the collector of the bipolar transistor have almost the same potential. Therefore, the voltage drop in the transistor seldom occurs while the bipolar transistor is activated, that is, at the moment of applying the voltage which is rectified by the load. Therefore, it is capable of efficient rectification with a small loss.
In the first to fifth inventions, the target voltage to be rectified may be an alternate signal or an alternate signal (a pulsating current) to which a direct current component is added, and its waveform may be any one of the sine wave, the triangle wave, the rectangular wave, or the like.
The meaning of xe2x80x9cconnectedxe2x80x9d here is not limited to xe2x80x9cwireboundxe2x80x9d. It includes cases of physical or electrical connection with the magnetism, an electric field, the light, or the like. For example, if a transistor, which is activated and inactivated in accordance with the amount of the light applied to its control terminal, is used, a control circuit and the control terminal are connected each other with the light. If a transistor which responds to the magnetic field of a Hall element, or the like, its control terminal and the control circuit are connected each other with the magnetic field.
The electric circuit according to a sixth aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and is controlled by said control circuit to be activated or inactivated to output rectified voltage to the other end of said current path; and
said control circuit, which is connected to at least one end of said current path of said transistor and said control terminal, makes said transistor rectify said target voltage to be rectified by controlling a signal to be applied to said control terminal to activate or inactivate said transistor so that said transistor is activated when a reverse voltage is applied to said current path and said transistor is inactivated when a forward voltage is applied to said current path,
said electric circuit is characterized in that said control circuit comprises:
a transformer comprising a primary winding to which electricity is provided, a secondary winding, which is inductively connected to said primary winding, for taking an output to be supplied to a load, and a detection winding, which is inductively connected to said primary winding, showing an output corresponding to an output of said secondary winding, and
detection means for inputting an output voltage of said secondary winding and an output voltage of said detection winding, for detecting whether said reverse voltage is applied to said current path and whether said forward voltage is applied to said current path, and for applying a signal indicating a result of the detection to said control terminal of said transistor.
The electric circuit according to a seventh aspect of the present invention comprises a transistor and a control circuit connected to said transistor, and is characterized in that said transistor comprises a current path and a control terminal, receives a target voltage to be rectified at one end of said current path, and is controlled by said control circuit to be activated or inactivated to output rectified voltage to the other end of said current path; and
said control circuit, which is connected to at least one end of said current path of said transistor and said control terminal, makes said transistor rectify said target voltage to be rectified by controlling a signal to be applied to said control terminal to activate or inactivate said transistor so that said transistor is activated when the reverse voltage is applied to said current path and said transistor is inactivated when the forward voltage is applied to said current path,
said electric circuit is characterized in that said control circuit comprises:
a first transformer comprising a primary winding to which an electricity is provided, and a second winding, which is inductively connected to said primary winding, for taking an output to be supplied to a load;
a second transformer, which is disposed being parallel to said first transformer while being insulated from said first transformer, comprising a first winding to which an electricity is provided, and a detection winding, which is inductively connected to said primary winding, showing an output corresponding to an output of said secondary winding of said first transformer; and
detection means for inputting an output voltage of said secondary winding and an output voltage of said detection winding, for detecting whether said reverse voltage is applied to said current path and whether said forward voltage is applied to said current path, and for applying a signal indicating a result of the detection to said control terminal of said transistor.
The electric circuits according to the sixth and the seventh aspects can rectify the alternate voltage output from the transformer.
The electric circuit according to an eighth aspect of the present invention comprises a semiconductor switching element and a control circuit for controlling said semiconductor switching element, and is characterized in that said semiconductor switching element comprises a current path whose one end is connected to a power source side and the other end is connected to a load side, and is controlled by said control circuit to be activated and inactivated; and
said control circuit is connected to both ends of said current path of said semiconductor switching element, detects voltage to be applied to said current path, and supplies a signal to said semiconductor switching element in accordance with a result of the detection to activate or inactivate said semiconductor switching element.
For example, a bipolar transistor, a field effect transistor, a photo transistor, a Hall element, a thyristor, or the like may be used as the semiconductor switching element.
The control circuit applies a control signal to the semiconductor switching element in accordance with the characteristics of the semiconductor switching element. For example, if the semiconductor switching element is the bipolar transistor, a voltage and a current to be supplied to base are controlled to activate and inactivate the bipolar transistor. If the semiconductor switching element is the field effect transistor, an electric field to be applied to gate is controlled to activate and inactivate the field effect transistor. If there is a gate electrode, voltage to be applied to the gate electrode is controlled. If the semiconductor switching element is the photo transistor, quantity (or strength) of the light to be irradiated to base is controlled to activate and inactivate the photo transistor. If the semiconductor switching element is the Hall element, a magnetic field (magnetic flux) is controlled to activate and inactivate the Hall element.